JP2009019274A - Production method of grain-oriented electromagnetic steel sheet with excellent adhesion to insulating film and extremely low core loss - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a tension-imparting insulating film with good adhesion on a grain-oriented electromagnetic steel sheet with no final annealed film to produce the grain-oriented electromagnetic steel sheet with extremely low core loss. <P>SOLUTION: The grain-oriented electromagnetic steel sheet with extremely low core loss has a coating layer composed of mainly SiO<SB>2</SB>via an oxide film of mainly SiO<SB>2</SB>formed by interface oxidation reaction on the surface of the steel sheet with no final annealed film and further has the tension-imparting insulating film on the surface of the coating layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention forms a high-strength insulating film with good adhesion on the surface of a grain-oriented electrical steel sheet that does not have a finish-annealed coating on the surface, and further on the surface of a grain-oriented electrical steel sheet that has been mirror-finished or after finishing annealing. And a method for producing a grain-oriented electrical steel sheet with extremely low iron loss by this method.

  Oriented electrical steel sheets are widely used as magnetic iron core materials, and in particular, a material with low iron loss is required to reduce energy loss. It is known that applying tension to a steel sheet is effective for reducing iron loss. In order to apply tension to the steel sheet, it is effective to form a film made of a material having a smaller thermal expansion coefficient than that of the steel sheet at a high temperature. A film mainly composed of forsterite (hereinafter referred to as finish annealing film) produced by the reaction of the oxide on the surface of the steel sheet and the annealing separator in the final annealing process has a high tension applied to the steel sheet and has a very good film adhesion. is there.

Furthermore, the method of forming an insulating film by baking a coating liquid mainly composed of colloidal silica, phosphate, and chromic acid disclosed in Patent Document 1 has a large effect of imparting tension to the steel sheet, and reduces iron loss. It is effective for. Further, Patent Document 2, as disclosed in Patent Document 3 or the like, it is coated with a coating solution obtained by mixing alumina sol and boric acid, aluminum borate coating film obtained by baking _{(Al x B y O 1.5 (} xy)), colloidal Gives a film tension of about 1.5 to 2 times that of an insulating film obtained from glassy silica, phosphate and chromic acid, and the effect of reducing iron loss is extremely large. Therefore, it is a general method for producing a grain-oriented electrical steel sheet to leave a film generated in the finish annealing process and to apply these tension-imparting type insulating films thereon.

  As a measure for reducing the iron loss of the grain-oriented electrical steel sheet, there has been proposed a method of forming grooves in a line shape or a point line shape substantially perpendicular to the rolling direction. Specific groove forming means include a method using mechanical means such as a grooved roll (Patent Document 4) and a method using chemical means such as etching (Patent Document 5).

  On the other hand, recently, it has become clear that the disordered interface structure between the finish annealed film and the ground iron cancels the film tension effect and the groove forming effect on the iron loss to some extent. Therefore, for example, as disclosed in Patent Document 6, after removing the finish annealing film, or after obtaining a grain-oriented electrical steel sheet mirror-finished during finish annealing by a method disclosed in Patent Document 7, Technology has been developed that attempts to further reduce iron loss by re-applying a tension coating.

However, the tension-applying type insulation film provides a good adhesion when applied on the finish annealed film, but does not remove the finish annealed film or intentionally form the film in the finish annealing process. In such a case, sufficient adhesion cannot be obtained. When the finish annealed film is removed, it is necessary to ensure the required film tension with only the insulating film, and it is necessary to increase the film thickness, and further film adhesion is required. Therefore, it is difficult to achieve a film tension enough to bring out the effect of mirroring with the conventional insulating film forming method. In order to solve such a problem, the inventors disclosed in Patent Document 8 a method of forming an external oxidation type SiO ₂ film by annealing a steel sheet in a weakly oxidizing atmosphere prior to forming an insulating film. According to this method, a tension-imparting insulating film can be formed with extremely good adhesion on a grain-oriented electrical steel sheet having no finish annealing film. However, in order to obtain stable film adhesion, a relatively high annealing temperature and a certain holding time are required, and the production cost must be increased.

  On the other hand, Patent Document 9 discloses a method of imparting adhesion to an insulating film of a grain-oriented electrical steel sheet without a finish annealing film by forming a gel film of 0.1 to 0.5 μm by a sol-gel method. Yes. However, the specific content disclosed in the publication is limited to the common-sense description regarding the formation of a thin film by the sol-gel method, and does not describe the conditions under which the adhesion can be reliably guaranteed.

Patent Document 10 discloses a method in which an aqueous phosphate or alkali metal silicate solution is applied at 4 g / m ² or less, baked at 350 ° C. or higher, and then an insulating film mainly composed of colloidal silica and phosphate is baked. Are listed. However, the adhesion obtained with this method is not stable, suggesting that some additional conditions are necessary.

Further, in Patent Document 11, a coating liquid containing an organometallic compound having a metal binding group such as alkoxysilane is applied, and then baked in an oxidizing atmosphere to generate Fe ₂ SiO ₄ at the interface with the iron. A method of forming a tension-imparting type insulating film by forming a coated film is disclosed. However, as will be described later, when Fe ₂ SiO ₄ is generated at the interface, an internal oxide layer is always generated inside the steel sheet, and the formation of the internal oxide layer results in a loss of adhesion and iron loss.

As described above, as for the coating-type intermediate layer forming technology that is easier to industrialize than the method of forming the SiO ₂ film by annealing, a method that can achieve both reliable adhesion and iron loss characteristics has been found. Absent.

JP 48-39338 A JP-A-6-65754 JP-A-6-65555 JP 61-117218 A JP-A-62-179105 JP-A 49-96920 JP-A-8-3648 JP-A-6-184762 Japanese Patent Laid-Open No. 3-130376 Japanese Patent Laid-Open No. 5-279747 JP 2002-235118 A

  In the grain-oriented electrical steel sheet without a forsterite film, the present invention is excellent in insulating film adhesion that reliably realizes adhesion of a tension-imparting type insulating film at low cost without impairing the obtained iron loss value, and A method for producing a grain-oriented electrical steel sheet with extremely low iron loss is provided.

  The present inventors have applied type intermediate layer method, that is, “form an intermediate layer by drying or baking after application to a grain-oriented electrical steel sheet without a finish annealing film, and then apply and bake a tension applying type insulating film”. The possibility of a low-cost film adhesion imparting method was investigated. For this purpose, it is necessary to find out the conditions for imparting adhesion to the coating-type intermediate layer. Therefore, various pretreatments are performed on the grain-oriented electrical steel sheet without the finish annealing film, and then various water-soluble silicates and silica After an intermediate layer was formed by coating drying or baking using colloids, an experiment was conducted systematically in which a tension applying type insulating film was baked, and the following important conclusions were obtained. In other words, good adhesion of the coating-type intermediate layer is realized based on a specific film structure, and additional conditions are necessary for forming the coating-type intermediate layer in order to obtain the specific film structure. It is.

FIG. 1 is a trigger for drawing the above conclusion. Fig. 1 shows the ground when a coating layer mainly composed of SiO ₂ is formed as a coating-type intermediate layer on a grain-oriented electrical steel sheet without a finish annealing film, and the tension-applying insulating film can be baked with good adhesion. It is a cross-sectional photograph by a transmission electron microscope near the iron-tension imparting insulating film interface.

  This steel plate was prepared by the following procedure. First, a grain-oriented electrical steel sheet having no finish annealing film was obtained by the method disclosed by the present inventors in Patent Document 7. Since this method is finally annealed in extremely pure hydrogen, the surface of the obtained grain-oriented electrical steel sheet has only a naturally formed oxide film of about 1 nm that cannot be visually confirmed. In FIG. 1 (a), this grain-oriented electrical steel sheet is washed with water and dried to form a thin rust layer (iron hydroxide layer) on the surface, and then tetraethoxysilane (TEOS) is hydrolyzed in an alcohol solvent to moderately with acid. A polymerized silica sol is applied and dried at a plate temperature of 200 ° C., and finally a tension-imparting insulating film mainly composed of phosphate and colloidal silica is applied and baked at 850 ° C. FIG. 1 (b) shows a directional electrical steel sheet without a finish annealed film immediately after finish annealing, coated with a lithium silicate aqueous solution and dried at a plate temperature of 200 ° C., and then a coating solution mainly composed of boric acid and alumina sol at 850 ° C. It is baked.

FIG. 1 (a), in either (b), the base steel, coating layer mainly composed of SiO _2, in addition to the insulating coating of the tension-imparting, observed a new film between the base steel -SiO ₂ layer . This new film is mainly composed of SiO ₂ and metal iron particles are observed.

From the above observation results, the present inventors obtained the following hypothesis. Before baking the tension-imparting type insulation film, iron oxide or iron hydroxide was formed at the interface between the base metal and the coating type intermediate layer. During baking of the insulating film, this iron oxide or iron hydroxide is used as the oxygen source, Si in the ground iron diffuses to the interface, and a thin oxide film mainly composed of SiO ₂ is formed between the SiO ₂ coating layer and the ground iron. It is considered that the formation of this thin oxide film strongly binds the SiO ₂ coating layer to the ground iron. The presence of metallic Fe is evidence that an interfacial oxidation reaction has occurred between the SiO ₂ coating layer and the ground iron.

The conditions for imparting adhesion in the coating-type intermediate layer method derived from this hypothesis are as follows. The coating-type intermediate layer must be fixed by an SiO ₂ film formed at the interface by some oxygen source and Si in the ground iron. Therefore, in order for a tension-imparting insulating film to be formed with good adhesion on a grain-oriented electrical steel sheet without a finish annealed film, it must have the following film structure. That is, in order from the base metal side, an oxide film mainly composed of SiO ₂ formed on the base metal by an interfacial oxidation reaction during baking, a coating layer mainly composed of SiO ₂ formed by coating and baking, and a tension applying insulating film It is. The correctness of this hypothesis was proved inductively by an example described later. The gist of the present invention is as follows.

(1) After applying iron oxide or iron hydroxide of 10 mg / m ² or less in terms of oxygen to a grain-oriented electrical steel sheet without a finish annealed film, a coating solution capable of forming a coating layer mainly composed of SiO ₂ is applied. After drying and forming a coating layer mainly composed of 0.01 to 1 g / m ² of SiO ₂ , a tension-imparting insulating film is formed with a coating solution containing a component that releases oxygen or water vapor at a temperature of 400 ° C. or higher. A method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion and extremely low iron loss, characterized in that it is formed.

  (2) The method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion and extremely low iron loss according to (1), wherein the component that releases oxygen or water vapor at a temperature of 400 ° C. or higher is alumina sol .

  (3) The insulating film according to (1) or (2), wherein the coating liquid containing a component that releases oxygen or water vapor at a temperature of 400 ° C. or higher is mainly composed of alumina sol and boric acid. A method for producing a grain-oriented electrical steel sheet having excellent adhesion and extremely low iron loss.

  (4) Any of (1) to (3), wherein the method of forming iron oxide on the grain-oriented electrical steel sheet surface without a finish annealed film is by annealing in air or nitrogen. A method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion and extremely low iron loss.

  (5) The method of forming iron hydroxide on the surface of a grain-oriented electrical steel sheet without a finish annealing film is characterized by water washing or light pickling and drying of the grain-oriented electrical steel sheet without a finish annealing film ( The manufacturing method of the grain-oriented electrical steel sheet which is excellent in the insulation film adhesiveness in any one of 1)-(3), and has an extremely low iron loss.

(6) The coating liquid capable of forming a coating layer mainly composed of SiO ₂ is any one of colloidal silica having a colloidal particle diameter of 10 nm or less, hydrolyzate of silicon alkoxide, sodium silicate aqueous solution, potassium silicate aqueous solution, or lithium silicate aqueous solution. Alternatively, the method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion and extremely low iron loss according to any one of (1) to (5), which is a mixture.

  (7) In any step before or after tension-applying insulation film baking after finish annealing or after baking of tension-applying insulation film, the width of the steel sheet surface is within a range of 45 ° from a right angle to the rolling direction. The insulating film adhesion according to any one of (1) to (6), wherein a linear or dot-like groove having a depth of 5 to 40 μm and a distance of 1 to 20 mm is formed. A method for producing grain-oriented electrical steel sheets with excellent and extremely low iron loss.

  Next, an embodiment of the present invention will be described.

  The present invention provides a good adhesion between the steel sheet surface and the insulating film when the insulating film capable of imparting high tension to the surface of the grain-oriented electrical steel sheet having no finish annealing film is formed. An intermediate film is formed to increase the adhesion between the insulating film and the steel sheet surface. Therefore, the target grain-oriented electrical steel sheet is a grain-oriented electrical steel sheet that has been subjected to a pickling treatment after finish annealing to remove the finish annealing film such as forsterite, or an additive is added to the annealing separator during finish annealing. Is a grain-oriented electrical steel sheet that suppresses the formation of a finish annealed film. Further, in order to obtain a magnetic steel sheet with low iron loss, a grain-oriented electrical steel sheet whose surface has been smoothed by means such as high-temperature annealing in a chemical or mechanical polishing or reducing atmosphere after removing the finish annealing film, Or a grain-oriented electrical steel sheet whose surface is smoothed by removing an oxide film at the time of primary recrystallization annealing and selecting an annealing separator other than MgO when finishing annealing, or alumina containing an alkali metal as an annealing separator, etc. A grain-oriented electrical steel sheet whose surface is smoothed by performing finish annealing using is used.

In addition, when heat-resistant magnetic domain control treatment is performed, that is, when a tension-imparting insulation film is formed on a directional electrical steel without a finish annealing film having grooves formed in a direction substantially perpendicular to the rolling direction by a grooved metal roll or electrolytic etching, etc. Is particularly suitable. As the shape of the groove, the direction of the groove is within a range of 45 ° perpendicular to the rolling direction, the width is preferably 10 to 300 μm, the depth is 5 to 40 μm, and the interval between the grooves is preferably 1 to 20 mm. Small iron loss improvement effect. The effect is the same regardless of whether the grooves are linear or dotted. The means for introducing grooves does not change the iron loss improvement effect or the adhesion development effect according to the present invention, regardless of mechanical or chemical means. In the present invention, the step of introducing the groove is not particularly limited. Any of the cold rolled sheet, the decarburized annealed sheet, and before and after the formation of the coating-type SiO ₂ layer after finish annealing can be performed.

  The present invention is applicable even when magnetic domain control is performed by laser irradiation on a grain-oriented electrical steel sheet having no finish annealing film. Since the laser irradiation effect disappears by heat treatment at 550 ° C. or higher, the laser irradiation is preferably performed after baking the tension-imparting insulating film.

The gist of the present invention is to set the film structure as follows in order to form a tension-imparting insulating film with good adhesion to a grain-oriented electrical steel sheet having no finish annealing film. That is, there is a coating layer mainly composed of SiO ₂ formed by coating and baking through an oxide film mainly composed of SiO ₂ generated by the interfacial oxidation reaction, and further, a tension applying type insulating film is present on the surface. It is something to be made. There are several means for realizing such a structure.

First, a coating solution capable of forming a coating layer mainly composed of SiO ₂ is applied and dried on the surface of a grain-oriented electrical steel sheet having no finish annealed film, and 0.01 to 1 g / m ² of SiO ₂ is mainly composed. After forming the coating layer, baking is performed at a plate temperature of 550 ° C. or more and 1200 ° C. or less in an atmosphere corresponding to a H ₂ O / H ₂ partial pressure ratio of 5 × 10 ⁻⁵ to 1 × 10 ⁻¹ , and tension is further applied. This is a method of applying and baking an application type insulating film (FIG. 2A). In the present invention, the baking atmosphere of the SiO ₂ coating layer is in the range of the H ₂ O / H ₂ partial pressure ratio of 5 × 10 ⁻⁵ to 1 × 10 ^−1. _It is not necessary to employ a _2— H ₂ O mixed atmosphere, and a CO—CO ₂ mixed gas may be used. What is important is that an oxide film mainly composed of SiO ₂ generated by an oxidation reaction is formed at the interface between the coating-type intermediate layer and the base iron during baking of the coating-type intermediate layer. During this interface reaction, Fe ₂ SiO It is to suppress generation of ₄ and FeO and generation of internal oxidation. Oxides such as Mn and Al are often observed in the oxide film generated by this interfacial oxidation reaction. These are due to the fact that grain-oriented electrical steel sheets often contain Mn, Al, etc. in addition to Si as alloy elements. To the SiO ₂ film produced by interfacial oxidation reaction of these Mn, oxides such as Al are present, rather than a layer of the SiO ₂ in which the film had been formed by coating baking mainly, produced by interfacial oxidation reaction It is proof that it is a thing. However, the presence of these oxides such as Mn and Al does not adversely affect the adhesion.

In the present invention, the baking temperature of the coating-type intermediate layer is set to 550 ° C. or more and 1200 ° C. or less. The reason why the temperature is set to 550 ° C. or higher is that, at a temperature lower than this, the diffusion rate of Si in the steel is small, so that formation of the SiO ₂ film hardly occurs. The reason why the upper limit is set to 1200 ° C. is that a heat treatment temperature exceeding 1200 ° C. is accompanied by a significant cost increase, and the steel sheet is softened, making it difficult to apply continuous annealing.

Patent Document 11 describes a method of baking a tensile film after applying and baking an organometallic compound such as silane coupling on a grain-oriented electrical steel sheet without a finish annealing film. The structure has completely different characteristics from that of the present invention. The baking conditions for the organometallic compound in this patent document are a steel plate temperature of 200 ° C. or higher and 800 ° C. or lower, and an oxygen partial pressure of 2 × 10 ⁻⁵ atm. On the other hand, the heat treatment conditions in the present invention are such that the steel sheet temperature is 550 ° C. or higher and the H ₂ O / H ₂ partial pressure ratio is in the range of 5 × 10 ⁻⁵ to 1 × 10 ⁻¹ .

The difference in the heat treatment conditions will be described in detail below. The oxygen partial pressure in the H ₂ O—H ₂ mixed atmosphere or CO ₂ —CO mixed atmosphere not containing oxygen can be estimated from the following equilibrium reaction. For example, in the case of an H ₂ O—H ₂ mixed atmosphere, if the equilibrium constant of the following reaction is K,
2H ₂ O = 2H ₂ + O ₂
The oxygen partial pressure P _O2 in the equilibrium state is P _O2 = K (P _H2O / P _H2 ) ²
Given in. FIG. 3 shows the equilibrium constant of the above equilibrium reaction. Referring to FIG. 3, the oxygen partial pressure in the present invention is approximately 10 ⁻⁴¹ to 10 ⁻¹² atm, which is completely different from the range 2 × 10 ⁻⁵ atm in Patent Document 11.

The above-mentioned difference in oxygen partial pressure gives a large difference in the generated oxide species and the oxide film structure. When silicon steel is heat-treated under the conditions of this patent document, not only Si but also Fe is oxidized. Therefore, the interfacial oxidation reaction product generated under the conditions described in the patent document is Fe ₂ SiO ₄ or FeO. In fact, the patent document describes that the formation of Fe ₂ SiO ₄ by an interfacial reaction is necessary for the expression of adhesion. In contrast, the interfacial oxidation reaction product required in the present invention is a film-like SiO ₂ as shown in FIG. Therefore, the interface structure disclosed in Patent Document 11 is completely different from that in the present invention. Further, when the surface of silicon steel is oxidized and Fe ₂ SiO ₄ is formed on the outermost surface, an internal oxide layer mainly composed of SiO ₂ is formed immediately below (N. Morito and T. Ichida). : Scripta Metallicica, vol. 10, p619-622 (1976)). The formation of the internal oxide layer not only deteriorates the iron loss of the grain-oriented electrical steel sheet, but also deteriorates the adhesion of the insulating film, as pointed out by the inventors in Patent Document 8. Therefore, the present invention is remarkably superior to the invention described in Patent Document 11 in terms of the obtained effect.

In the second method, an iron oxide or iron hydroxide layer is formed on a grain-oriented electrical steel sheet having no finish annealing film, and then a coating solution capable of forming a coating layer mainly composed of SiO ₂ is 0.01 to 1 g / m. ^{2 A} method of applying and baking a tension-applying type insulating film after coating and drying (FIG. 2B). As a means for forming iron oxide or iron hydroxide, a method of drying after annealing, water washing or light pickling can be employed.

In the case of this method, the range of iron oxide and iron hydroxide formation varies depending on the type of insulating film to be baked thereafter. In the case of an insulating film mainly composed of colloidal silica and phosphate, the amount of iron oxide and iron hydroxide formed is 5 to 100 mg / m ² in terms of oxygen. On the other hand, when alumina sol is contained in the coating solution, for example, when it is mainly composed of alumina sol and boric acid, there is no lower limit to the amount of iron oxide and iron hydroxide, and it is 10 mg / m ² or less in terms of oxygen. This is because the moisture released from the alumina hydrate during baking of the insulating film can be used as an oxygen source for the interfacial oxidation reaction. When the oxide and hydroxide formation amount exceeds the above range, the interfacial oxidation reaction becomes abnormal, and adhesion to the tension-imparting insulating film is not exhibited.

When this second method is used, an oxide such as Mn or Al may be formed in the SiO ₂ film generated by the interface oxidation reaction, as in the case of using the first method. Further, as shown in FIG. 1B, the Fe ₂ particles may be contained in the SiO ₂ film. The presence of these components other than SiO ₂ has no adverse effect on the adhesion. The presence of metallic Fe particles effectively acts as an oxygen source for the interfacial oxidation reaction while iron oxide or iron hydroxide is once generated on the steel sheet surface during the coating and baking process of the coating-type intermediate layer, and these are reduced during the baking process. It shows that it did.

In both the first and second methods, a coating solution that can form a coating layer mainly composed of SiO ₂ is applied and dried prior to application of the insulating film. However, the coating solution and the coating amount are also limited. First, the size of the silica colloid particles in the coating solution must be 10 nm or less. This is because if it is larger than this, a dense SiO ₂ coating layer cannot be obtained. The formation amount of the SiO ₂ coating layer needs to be 0.01 to 1 g / m ² . This is because if it is less than this, the SiO ₂ coating layer is not uniform, whereas if it is more than this, a dense layer cannot be formed.

The amount of the SiO ₂ coating layer formed after coating and drying can be determined by immersing the steel sheet in a hot sodium hydroxide aqueous solution to remove the coating layer, and measuring the change in the weight of the steel sheet before and after the removal. It is also possible to obtain the thickness of the SiO ₂ coating layer by observing the cross section with a transmission electron microscope and to calculate using the fact that the density of the substance mainly composed of SiO ₂ is about 2 g / cm ^3. .

As a coating liquid suitable for forming a coating-type SiO ₂ coating layer, colloidal silica, silica sol liquid prepared by hydrolyzing tetraethoxysilane, or alkali metal silicate may be used, but 0.01 to 1 g If a dry film mainly composed of dense SiO ₂ / m ² is obtained, it is not necessary to limit to the above. As a matter of course, when an alkali metal silicate is used as a coating solution for forming a SiO ₂ coating layer, the coating layer contains an alkali metal in an oxide state.

Patent Document 9 discloses a technique using a sol-gel method as a method for forming an insulating film with good adhesion on a grain-oriented electrical steel sheet having no finish annealing film. However, this specification does not describe the formation of the SiO ₂ film generated by the interfacial oxidation reaction disclosed in the present invention. Also, it is clear from the description of the specification that such a reaction film is not formed by the method described in the specification of the patent document.

  In the specification of Patent Document 9, two specific methods are listed. One is a method in which a gel film is formed at a temperature of about 100 ° C. and then a tension applying type insulating film is baked. The tension-imparting type insulating film known at the time when the specification of the patent document was disclosed is mainly composed of colloidal silica and phosphate, as shown in Examples of the specification. When the coating-type intermediate layer is kept dry and an insulating film mainly composed of colloidal silica and phosphate is applied, a thin iron oxide or iron hydroxide is formed prior to the formation of the coating-type intermediate layer, that is, the sol-gel film. However, there is no description suggesting such processing in the specification.

Another method disclosed in the specification of this patent document is a method of baking an insulating film after baking a sol-gel film once. There are descriptions of 450 ° C. and 500 ° C. as specific temperatures in this case. As described in the present invention, when the baking temperature of the coating-type intermediate layer, that is, the sol-gel film is lower than 550 ° C., the SiO ₂ film formation due to the interface oxidation reaction does not occur. In addition, in order to form an interfacial oxide SiO ₂ film that effectively acts on adhesion, it is necessary to set the atmosphere strictly in addition to the temperature, but this specification does not include any such description. No.

From the above, in the method disclosed in Patent Document 9, the SiO ₂ film generated by the interfacial oxidation reaction claimed in the present invention is not formed, and therefore the adhesion to the tension-applying insulating film is the present invention. It is thought that it is inferior to what was disclosed in.

The present invention, in order to good adhesion to form a tension-imparting insulating coating to not oriented electrical steel sheet finish annealing film, SiO ₂ via the oxide film mainly made of SiO ₂ produced by interfacial oxidation reaction This proves that the structure in which the coating layer mainly composed of is formed is effective. Hereinafter, specific means for obtaining such an interface structure and the effects thereof will be described with reference to examples.
(Example)
By the method according to Patent Document 7, a grain-oriented electrical steel sheet having a finish annealing film having a thickness of 0.22 mm and having a mirror surface is prepared. A silica sol obtained by hydrolyzing sodium silicate and tetraethoxysilane, and a commercially available silica sol were prepared. In the case of the silica sol by tetraethoxysilane hydrolysis, the condensing conditions were adjusted and different silica colloid particle diameters were prepared. Commercially available silica sols with different colloidal particle sizes were also prepared. These silica colloidal solutions were applied to the steel sheet in various coating amounts and dried at 200 ° C. Next, an insulating film coating solution mainly composed of alumina sol and boric acid was applied and baked at 850 ° C. (film amount 4 g / m ² ). Table 1 shows the results of evaluating the adhesion of these samples.

According to Table 1, when the colloidal particle diameter exceeds 10 nm as the silica colloid for forming the coating layer mainly composed of SiO ₂ or when the coating amount exceeds 1 g / m ² , the coating layer is formed on the steel plate. Is difficult to understand. It can also be seen that when the SiO ₂ coating layer formation amount is less than 0.01 g / m ² , the insulating film adhesion cannot be obtained. If the amount of the SiO ₂ coating layer formed is insufficient, the surface cannot be uniformly coated, and the interface oxidation during baking is assumed to be non-uniform.

  According to the present invention, it is possible to form a tension-imparting insulating film with good adhesion to a grain-oriented electrical steel sheet without a finish annealed film, and to obtain a grain-oriented electrical steel sheet with extremely low iron loss at low cost. In addition, it greatly contributes to the development of the electrical industry, which is a consumer of steel sheets.

(A), (b) is a cross section of the vicinity of the iron-insulation coating interface by a transmission electron microscope when a tension-imparting insulating coating is formed on a grain oriented electrical steel sheet without a finish annealing coating with good adhesion. Photo. (A), (b) is a schematic view showing a process of SiO ₂ oxide film by interfacial oxidation reaction is formed on the coating-type interlayer and the base steel interface. Figure shows the temperature dependence of the equilibrium constant K in _{2H 2 O = 2H 2 + O} 2 equilibrium reaction.

Claims (7)

After forming iron oxide or iron hydroxide of 10 mg / m ² or less in terms of oxygen on a grain-oriented electrical steel sheet without a finish annealed coating, a coating solution capable of forming a coating layer mainly composed of SiO ₂ is applied and dried. After forming a coating layer mainly composed of 0.01 to 1 g / m ² of SiO ₂ , a tension-imparting insulating film is formed with a coating solution containing a component that releases oxygen or water vapor at a temperature of 400 ° C. or higher. A method for producing a grain-oriented electrical steel sheet having excellent adhesive film adhesion and extremely low iron loss.   The method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion and extremely low iron loss according to claim 1, wherein the component that releases oxygen or water vapor at a temperature of 400 ° C or higher is alumina sol.   The coating solution containing a component that releases oxygen or water vapor at a temperature of 400 ° C or higher is mainly composed of alumina sol and boric acid, and has excellent insulating film adhesion as set forth in claim 1 or 2. A method for producing grain-oriented electrical steel sheets with extremely low iron loss.   The method of forming iron oxide on a grain-oriented electrical steel sheet surface without a finish annealing film is based on annealing in the atmosphere or nitrogen, wherein the insulating film adheres according to any one of claims 1 to 3. For producing grain-oriented electrical steel sheets with excellent properties and extremely low iron loss.   The method for forming iron hydroxide on the surface of a grain-oriented electrical steel sheet without a finish annealing film is by water washing or light pickling and drying of the grain-oriented electrical steel sheet without a finish annealing film. 4. A method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion according to any one of claims 3 and extremely low iron loss. The coating liquid capable of forming a coating layer mainly composed of SiO ₂ is any one or a mixture of colloidal silica having a colloidal particle diameter of 10 nm or less, hydrolyzate of silicon alkoxide, sodium silicate aqueous solution, potassium silicate aqueous solution, lithium silicate aqueous solution. The method for producing a grain-oriented electrical steel sheet having excellent insulating film adhesion and extremely low iron loss according to any one of claims 1 to 5.   In any step before or after tension-applying insulation film baking after finish annealing, or after baking tension-applying insulation film, the width of the steel sheet is 10 to 300 μm within a range of 45 ° from the direction perpendicular to the rolling direction, 7. A linear or dot-like groove having a depth of 5 to 40 [mu] m and an interval of 1 to 20 mm is formed, and has excellent insulation film adhesion and iron loss according to any one of claims 1 to 6 A manufacturing method for extremely low grain-oriented electrical steel sheets.